Rectifying and amplifying circuits



Jan. 28, 1941. "c. L. RICHARDS RECTIFYING AND AMPIIIFYING CIRCUITS Filed June 8, i937 INVENTOR (Ml/DE MN MN RICHARDS BY g ATTORNEY Patented Jan. 28, 1941 UNITED STATES PATENT OFFICE Claude Langdon Richar lands, assignor, by me dio Corporation of Am ds, Eindhoven, Nethersne assignments, to Raerica, New York, N. Y., a

corporation of Delaware Application June 8, 1937, Serial No. 147,000 In Germany June 13, 1936 2 Claims. (01. 250-20) The invention relates to a circuit-arrangement for rectifying modulated high or intermediate frequency oscillations and for amplifying the low frequency oscillations obtained after rectification, and more particularly to a circuit arrangement adapted to amplify a very broad band of frequencies.

The need for such a circuit arrangement is particularly prevalent with the present day tele- 1 vision receivers with which the low frequency picture currents to be supplied to the reproducing device include, together with the synchronizing impulses, a very broad band of frequencies, for example from to 2x10 cycles.

In practice it has been found that with the known circuit arrangements which are adapted to rectify high or intermediate frequency oscillations and to amplify the low frequency oscillations obtained after rectification, no satisfactory results are obtained. If a diode is utilized for rectification, there arises the drawback that an insufficient output voltage for the high frequencies is obtained. On the other hand, the lowest modulation frequencies can only be maintained 25 if after the detector a direct current amplifier is provided. A generally known drawback of direct current amplifiers resides however in that the cathodes of the amplifying tubes have different voltages relatively to one another and to the earth and therefore have to be insulated with respect to one another and to the earth.

The invention has for its object to provide a circuit arrangement with which the output voltage has a sufficiently high value for the highest modulation frequencies and which has the advantages of the known circuit arrangements but not the disadvantages thereof.

According to the invention, the oscillations to be rectified are supplied on the one hand to a discharge tube which is connected as an anode detector and which is coupled, by means of a coupling element which does not pass the low frequencies, with an alternating current amplifier consisting of one or more stages, and on the other hand to a diode whose output voltage is applied, via a filter which passes the said low frequencies, to the grid of the last amplifying tube of the alternating current amplifier in such manner that with an increasing amplitude of the carrier wave of the oscillations to be rectified the direct current voltage of the grid becomes more negative.

With the circuit arrangement according to the invention the last tube of said alternating ourrent amplifier should preferably have an a proximately rectilinear characteristic curve.

My invention will best be understood by refer-, ence to the drawing in which Fig. 1 shows one embodiment thereof;

Fig. 2 shows another embodiment thereof.

The circuit arrangement shown in Fig, 1 com- I prises a high or intermediate frequency amplifying tube V1, a tube V2 connected as an anode detector, a low frequency amplifying tube V3 and a diode D. The oscillations to be rectified which are set up between terminals 2 and 4 are supplied to the grid of the high or intermediate frequency amplifying tube V1, which may be the last high or intermediate frequency amplifying tube of a television receiver. The output circuit of the tube V1 includes a filter F through which the high or intermediate frequency oscillations are supplied on the one hand to the diode D and on the other hand to the tube V2 connected as an anode detector.

The circuit, which comprises the output circuit of the filter F and the diode D, includes the parallel connection of a resistance 6 and of a condenser 8, across which parallel connection the oscillations rectified by means of the diode D occur. That end of the resistance 6 which is not connected to the cathode of the tube D is connected via a low-pass filter which passes the low frequencies of the band of frequencies to be amplified, or at least the direct current components, and which comp-rises a resistance l0 and a condenser [2, to the grid of the amplifying tube V3 owing to which the voltage set up across the resistance 6 is supplied to the grid of the amplifying tube Va.

The oscillations produced in the output circuit of the filter F are further supplied via a coupling condenser l4 and a resistance-l6 to the grid of the tube V2. That part of the anode circuit 40 which is common to the grid and anode circuits of the tube V2 includes the parallel connection of aresistance I 8 and of a condenser 20 which serve to obtain the grid bias of the tube V2 which is required for anode rectification. The tube V2 is connected to the low frequency amplifying tube V3 via a coupling element which comprises resistances 22 and 24 and a condenser 26. The coupling element 22, 24, 26 is so dimensioned that the low frequencies of the band of frequencies to be amplified or at least the direct current component, are not supplied to the grid of the tube V The output circuit of the tube W includes a resistance 28 across which a voltage is set up frequencies occur in which may be supplied to a load, for example to the reproducing device of a television receiver.

The modulated high or intermediate frequency oscillations supplied to the terminals 2 and 4 are rectified by that part of the circuit arrangement which is formed by the tube V2, the coupling element 22, 2d, 26 and the low frequency amplifying tube V3 and of the low frequency oscillations thus obtained are amplified only those frequencies which are located above the passband of the coupling element 22, 24, 2B.

In order to ensure that the low frequency oscillations whose frequencies are located below the pass-band of said part of the circuit arrangement are set up in the output circuit of the circuit arrangement between the terminals 30 and 32, the diode D as well as the filter l8, 12 have been provided. Through said part of the circuit arrangement there is supplied to the grid of the amplifying tube V3 a variable negative bias voltage whose amplitude depends on the low frequency voltage across the resistance '6 and whose frequency is determined by the pass-band of the filter l0, l2. The filter H3, I2 is arranged in such manner that only those frequencies of the low frequency oscillations set up at the resistance 6 which are located below the pass-band of the coupling element 22, 24, 28 are applied to the grid of the tube V3 with the result that these the output circuit of the tube V3 between the terminals 3!! and 32.

The output voltage of the diode is supplied to the grid of the tube V3 in the correct phase if with an increase of the carrier wave amplitude of the oscillations supplied to the diode the grid bias of the tube V becomes more negative, or in other words the anode direct current of the tube V3 decreases and consequently the voltage across the terminals 38 and 32' increases. The increase 5 of the carrier wave amplitude results in fact from an increase of the direct current component which is modulated on the carrier wave and which is lost in that part of the circuit arrangement which is formed by the tube V2, the coupling element 22, 24, 26 and the amplifying tube V3.

Fig. 2 represents a form of construction wherein the oscillations supplied to the terminals 2 and 4 are supplied via a high or intermediate frequency amplifying tube V1 and a filter F1 to the tube V2 connected as an anode detector and via a second high or intermediate frequency amplifying tube V1 and a filter F2 to a diode D. The advantage attending the use of separate high or intermediate frequency amplifying tubes resides in that the frequency band which is passed by the filters F1 and F2 may be adapted to that part of the circuit arrangement which is located after said filter. The circuit arrangement should preferably be such that the whole of the band of frequencies received is uniformly transmitted by the filter F1 and that solely the direct current component of the modulation is lost in that part of the circuit arrangement which is formed by the tube V2, the coupling element 22, 24, 26 and the tube V3 whereas the pass-band of the filter F2 is narrow and only the direct-current component is applied via the filter Ill, l2 to the grid of the tube V3.

An appreciable advantage which attends the use of the circuit-arrangement of Fig. 2 when used in a television receiving system consists in that through the filter F2 a frequency band which includes the frequency of the synchronizing impulses may be supplied to the diode D. The synchronizing impulses may be taken in this case from the resistance 6; the direct-current component of the synchronizing impulses is not lost in this case as would be the case if these impulses were taken from that part of the circuit arrangement which is located after the detector tube V2.

With the circuit arrangements shown the alternating current amplifier comprises only one amplifying tube V3. In order to obtain a greater amplification of the high frequencies use may be made of any desired number of amplification stages. Independently of the number of stages the output voltage of the diode is supplied in the circuit arrangement according to the invention to the last amplifying tube of the alternating current amplifier because the alternating current amplifier is not adapted to amplify the frequency components supplied to the amplifier via the filter l0, [2.

The last amplifying tube of the alternating current amplifier should preferably have a rectilinear grid voltage anode current characteristic curve as in the case of a curved characteristic a variation of the grid bias results not only in a variation of the anode direct current but also in an alteration of the amplification of the tube. This alteration of the amplification is such that with an increasing amplitude of the carrier oscillation the amplification decreases and conversely, which is not desirable with the circuit arrangement according to the invention.

The initially mentioned drawback which attends the use of a diode and which consists in that the output voltage of such a tube has not a sufficiently high value for the high modulation frequencies does not arise with the circuit arrangement according to the invention owing to the fact that the diode D exclusively serves to obtain the low modulation frequencies or at least the direct current component. The capacitative impedance of the diode is, however, large for these frequencies.

What I claim is:

1. An amplifying circuit comprising a signal source to supply alternating current energy of frequencies varying between relatively high values and extremely low values, a pair of parallelly connected rectifying means connected to receive the supplied signal from said source, a low frequency cut-off filter circuit connected to the output of one of said rectifying means, a low pass filter connected to receive the output of the other of said rectifying means, an amplifying tube capacitively connected to the low frequency cutoff filter to amplify the rectified output of the first of said rectifying means and means for controlling the amplification level of said amplifier under the control of the signals passed through said low pass filter as rectified by the second of said rectifying means.

2. An amplifying and detecting circuit comprising a signal source for supplying alternating current wave energy including frequencies varying between the substantially zero frequency and a frequency of the order of at least two megacycles, a parallelly connected multi-electrode rectifying tube and a diode rectifying tube connected to receive the signal energy from said signal source, said connection to the mutli-electrode rectifying tube input including a capacity element, a low frequency cut-off filter connected to the output of the multi-electrode rectifying tube, an amplifying tube, means for capacitively coupling said amplifying tube to the output of the multi-electrode rectifying tube whereby the said rectified signals may be amplified, a low-pass filter circuit connected to receive the output of the diode rectifying means, a connection between the input circuit of said amplifying tube and the output of said diode rectifying means for biasing the said amplifier tube in accordance with the rectified signal energy passed by said low-pass filter and rectified by said diode, whereby the amplification level of the said amplifier means is controlled in accordance with the low frequency components of the received signal energy, and a load circuit connected to the output of the said amplifier means.

CLAUDE LANGDON RICHARDS. 

